Automobile assembly lines are provided, for example, with articulated robots such as the one disclosed in Japanese Patent Laid-Open Publication No. 6-71581. Articulated robots have servomotors and decelerators provided to all of the joints, and the joints can therefore be operated independently.
When problems occur with the bearing that supports the motor axle or the decelerator axle in a servomotor or a decelerator, the motor axle or the decelerator axle does not rotate smoothly. When the axle does not rotate smoothly, the distal end of the robot arm is displaced from a target position.
Since it is not difficult to detect the positional displacement, any malfunction in the articulated robot can be easily detected. However, in such cases, it is not possible to identify which joint among multiple joints is undergoing problems. If the articulated robot has six joints, the robot must be stopped, and a series of failure prevention measures must be taken for each of six locations. In these measures, the servomotors or the decelerators are inspected, the breakdown locations are pinpointed, parts are replaced, and teaching and positional corrections are carried out. This series of failure prevention measures is time consuming and therefore leads to a decrease in productivity.
In view of this, a need has arisen to develop an apparatus for monitoring the joints of an articulated robot, wherein it is possible to specify which joint is undergoing problems.